1. Field of the Invention
The present invention relates generally to timing control of transceiver, in particular to all-digital timing control for multi-channel full-duplex transceiver.
2. Description of Related Art
As depicted in FIG. 1, a full-duplex communication system 100 comprises a first transceiver 110, a second transceiver 120, and a communication media 130. The first (second) transceiver 110 (120) comprises a transmitter 112 (124), a receiver 114 (122), and a duplexer 116 (126). The first transceiver 110 receives a first transmitting data TX1, encodes/modulates the data into a first electrical signal S1 suitable for transmission over the communication media 130 unto the second transceiver 120 using transmitter 112. The second transceiver 120 receives the first electrical signal S1 via duplexer 116, the communication media 130, and duplexer 126, and then decodes/demodulates the received electrical signal into a first receiving data RX1 using receiver 122. In the mean while, the second transceiver 120 receives a second transmitting data TX2, encodes/modulates the data into a second electrical signal S2 suitable for transmission over the communication media 130 unto the first transceiver 110 using transmitter 124. The first transceiver 110 receives the second electrical signal S2 via duplexer 126, the communication media 130, and duplexer 116, and then decodes/demodulates the received electrical signal into a second receive data RX2 using receiver 114. If both transceivers work perfectly, the first receiving data RX1 should match the first transmitting data TX1, while the second receiving data RX2 should match the second transmitting data. For the first (second) transceiver 110 (120), the purpose of the duplexer 116 (126), which is normally embodied by a hybrid circuit, is to allow the transmitter 112 (124) to launch an outgoing electrical signal into the communication media 130 while at the same time allow the receiver 114 (122) to receive an incoming electrical signal from the communication media 130.
A modulation scheme of particular interest to the present invention is PAM (pulse amplitude modulation), while employs a multi-level electrical signal to represent data. For instance, a PAM-4 transmitter generates a 4-level electrical signal {−3, −1, 1, 3} to represent a two-bit data. A PAM-4 receiver, on the other hand, detects the two-bit data in accordance of the level of the received electrical signal.
To boost the amount of data that can be communicated, sometimes a plurality of channels is used for the communication media. For instance, a 4-channel communication media allows approximately four times more information to be communicated, compared to a single channel communication media, provided every one of the four channels is substantially identical to the single channel. In this case, there must be 4 transmitters, 4 receivers, and 4 duplexers in a transceiver for transmitting four sets of outgoing data and detecting four set of incoming data via the four channels, respectively.
This present invention is related to multi-channel full-duplex PAM transceiver. Throughout this disclosure, the term “local transceiver” is used to refer to one of the two transceivers involved in a full-duplex communication, and the term “remote transceiver” is used to refer to the other one of the two transceivers.
There are a few issues that need to be addressed in a multi-channel full-duplex PAM transceiver. First, the communication channel usually introduces certain distortion to the multi-level electrical signal. To correct the distortion, a function known as “equalization” is usually needed. Second, the timing with respect to which the transmitter of the remote transceiver transmits the multi-level signal is unknown. To estimate the timing, a function known as “timing recovery” is needed. Third, due to simultaneous transmitting and receiving, an interference known as “echo” originated from the transmitter of the local transceiver enters into the receiver of the local transceiver for the same channel. To alleviate this interference, a function known as “echo cancellation” is needed. Fourth, due to using multiple channels, an interference known as “NEXT” (“near-end cross talk”) originated from the transmitter of the local transceiver of one channel enters into the receiver of the local transceiver of another channel. To alleviate this interference, a function known as “NEXT cancellation” is needed. Fifth, an interference known as “FEXT” (“far-end cross talk”) originated from the transmitter of the remote transceiver of one channel enters into the receiver of the local transceiver of another channel. To alleviate this interference, a function known as “FEXT cancellation” is needed.
A communication standard known as “10 GBase-T” is closely related to the scope of the present invention. 10 GBase-T uses four twist pairs as communication media. Also, 10 GBase-T uses a modulation scheme known as “DSQ-128,” which can be viewed as a special type of PAM. 10 GBase-T uses a special type of transmitter-side equalization known as “THP pre-coder” to pre-equalize the multi-level signal for compensating beforehand the distortion expected to be caused by the twist pair. Besides, between the two transceivers involved in a 10 GBase-T communication link, one must act as “master” while the other must act as “slave.” The master transceiver transmits data to the slave transceiver in a timing (and data rate) that the master transceiver determines itself. The slave transceiver must detect the timing (and data rate) and base on the same timing (and data rate) to transmit data to the master transceiver.
What is needed is a method of timing control for a 10 GBase-T transceiver, be it master or slave.